My cookbook about how to get the essence of that article is simple, locate in your /etc/fstab file the line:

/dev/mmcblk0p2 / ext4 defaults,noatime 0 1

and modify that line with:

/dev/mmcblk0p2 / ext4 defaults,noatime,ro 0 1

After rebooting your system is going to work in read-only mode. I don’t remember if I modified anything else of the booting process but I don’t thing so.
Because sometimes I have to modify anything in the flash card, I added the next two lines in the ~/.bashrc file: